Bonded body, substrate for power module with heat sink, heat sink, method for producing bonded body, method for producing substrate for power module with heat sink, and method for producing heat sink

ABSTRACT

A bonded body is provided that is formed by bonding a metal member formed from copper, nickel, or silver, and an aluminum alloy member formed from an aluminum alloy of which a solidus temperature is lower than a eutectic temperature of aluminum and a metal element that constitutes the metal member. The aluminum alloy member and the metal member are subjected to solid-phase diffusion bonding. A chill layer, in which a Si phase of which an aspect ratio of a crystal grain is 2.5 or less and a crystal grain diameter is 15 μm or less is dispersed, is formed on a bonding interface side with the metal member in the aluminum alloy member. The thickness of the chill layer is set to 50 μm or greater.

TECHNICAL FIELD

The present invention relates to a bonded body that is formed by bondinga metal member formed from copper, nickel, or silver to an aluminumalloy member formed from an aluminum alloy of which a solidustemperature is lower than a eutectic temperature of aluminum and a metalelement that constitutes the metal member, a power module substrate withheat sink which includes a power module substrate and a heat sink, aheat sink including a heat sink main body and a metal member layer, amethod of manufacturing a bonded body, a method of manufacturing a powermodule substrate with heat sink, and a method of manufacturing a heatsink.

Priority is claimed on Japanese Patent Application No. 2015-084029,filed on Apr. 16, 2015, and Japanese Patent Application No. 2016-033201,filed on Feb. 24, 2016, the contents of which are incorporated herein byreference.

BACKGROUND ART

A semiconductor device such as an LED and a power module is providedwith a structure in which a semiconductor element is bonded onto acircuit layer formed from a conductive material.

In a large-power control power semiconductor element that is used tocontrol wind power generation, an electric vehicle, a hybrid car, andthe like, the amount of heat generation is great. According to this, asa substrate on which the large-power control power semiconductor elementis mounted, for example, a power module substrate including a ceramicsubstrate formed from aluminum nitride (AlN), alumina (Al₂O₃), and thelike, and a circuit layer formed by bonding a metal plate with excellentconductivity on one surface of the ceramic substrate has been widelyused in the related art. Furthermore, as the power module substrate, apower module substrate, in which a metal layer is formed on the othersurface of the ceramic substrate, is also provided.

For example, a power module disclosed in PTL 1 has a structure includinga power module substrate in which a circuit layer and a metal layerwhich are formed from Al are respectively formed on one surface and theother surface of a ceramic substrate, and a semiconductor element thatis bonded onto the circuit layer through a solder material.

In addition, a heat sink is bonded to a metal layer side of the powermodule substrate to radiate heat, which is transferred from thesemiconductor element to the power module substrate side, to an outerside through the heat sink.

However, as is the case with the power module described in PTL 1, in acase where the circuit layer and the metal layer are constituted by Al,an oxide film of Al is formed on a surface, and thus it is difficult tobond the semiconductor element or the heat sink onto the surface withthe solder material.

Accordingly, in the related art, for example, as disclosed in PTL 2,after a Ni plating film is formed on the surface of the circuit layerand the metal layer through electroless plating and the like, thesemiconductor element or the heat sink is subjected to solider-bonding.

In addition, PTL 3 suggests a technology of bonding the circuit layerand the semiconductor element, and the metal layer and the heat sink,respectively, by using silver oxide paste containing a reducing agentincluding silver oxide particles and an organic material as analternative of the solder material.

However, as described in PTL 2, in the power module substrate in whichthe Ni plating film is formed on the surface of the circuit layer andthe metal layer, during bonding of the semiconductor element and theheat sink, a surface of the Ni plating film deteriorates due tooxidation and the like, and thus there is a concern that bondingreliability of the semiconductor element and the heat sink which arebonded through the solder material deteriorates. Here, when bondingbetween the heat sink and the metal layer is not sufficient, there is aconcern that heat resistance increases, and thus heat dissipationcharacteristics deteriorate. In addition, in a Ni plating process, amasking process may be performed in order prevent problems such aselectrolytic corrosion due to formation of the Ni plating in anunnecessary region from occurring. As described above, in a case ofperforming a plating process after performing the masking process, agreat deal of labor is necessary in the process of forming the Niplating film on the surface of the circuit layer and the surface of themetal layer, and thus there is a problem in that the manufacturing costof the power module greatly increases.

In addition, as described in PTL 3, in a case of respectively bondingthe circuit layer and the semiconductor element, and the metal layer andthe heat sink by using the silver oxide paste, bondability between Aland a baked body of the silver oxide paste is poor, and thus it isnecessary to form a Ag underlying layer on the surface of the circuitlayer and the surface of the metal layer in advance. In a case offorming the Ag underlying layer through plating, there is a problem inthat a great deal of labor is necessary similar to Ni plating.

Accordingly, PTL 4 suggests a power module substrate in which thecircuit layer and the metal layer are set to have a laminated structureof an Al layer and a Cu layer. In the power module substrate, the Culayer is disposed on the surface of the circuit layer and the metallayer, and thus it is possible to bond the semiconductor element and theheat sink by using a solder material in a satisfactory manner. As aresult, heat resistance in a laminating direction decreases, and thus itis possible to transfer heat, which is generated from the semiconductorelement, to the heat sink side in a satisfactory manner.

In addition, PTL 5 suggests a power module substrate with heat sink inwhich one of the metal layer and the heat sink is constituted byaluminum or an aluminum alloy, the other side is constituted by copperor a copper alloy, and the metal layer and the heat sink are subjectedto solid-phase diffusion bonding. In the power module substrate withheat sink, the metal layer and the heat sink are subjected to thesolid-phase diffusion bonding, and thus heat resistance is small, andheat dissipation characteristics are excellent.

CITATION LIST Patent Literature

[PTL 1] Japanese Patent Publication No. 3171234

[PTL 2] Japanese Unexamined Patent Application, First Publication No.2004-172378

[PTL 3] Japanese Unexamined Patent Application, First Publication No.2008-208442

[PTL 4] Japanese Unexamined Patent Application, First Publication No.2014-160799

[PTL 5] Japanese Unexamined Patent Application, First Publication No.2014-099596

DISCLOSURE OF INVENTION Technical Problem

However, in a heat sink having a complicated structure in which a flowpassage of a cooling medium and the like are formed on an inner side,the heat sink may be manufactured with a casted aluminum alloy having arelatively low solidus temperature.

Here, in a case of subjecting the aluminum alloy member formed from thecasted aluminum alloy having the low solidus temperature, and the metalmember formed from copper or a copper alloy to the solid-phase diffusionbonding as described in PTL 5, it is confirmed that a lot of Kirkendallvoids, which occur due to unbalance of mutual diffusion, occur in thevicinity of a bonding interface. When the Kirkendall voids exist betweenthe power module substrate and the heat sink, heat resistance increases,and thus there is a problem in that heat dissipation characteristicsdeteriorate.

The invention has been made in consideration of the above-describedcircumstances, and an object thereof is to provide a bonded body inwhich an aluminum alloy member formed from an aluminum alloy having arelatively low solidus temperature, and a metal member formed fromcopper, nickel, or silver are bonded to each other in a satisfactorymanner, and heat resistance in a laminating direction is low, a powermodule substrate with heat sink and a heat sink which include the bondedbody, a method of manufacturing a bonded body, and a method ofmanufacturing a power module substrate with heat sink, and a method ofmanufacturing a heat sink.

SOLUTION TO PROBLEM

To solve the above-described problem, according to an aspect of theinvention, a bonded body is provided, formed by bonding a metal memberformed from copper, nickel, or silver, and an aluminum alloy memberformed from an aluminum alloy of which a solidus temperature is lowerthan a eutectic temperature of aluminum and a metal element thatconstitutes the metal member. The aluminum alloy member and the metalmember are subjected to solid-phase diffusion bonding. A chill layer, inwhich a Si phase of which an aspect ratio of a crystal grain is 2.5 orless and a crystal grain diameter is 15 μm or less is dispersed, isformed on a bonding interface side with the metal member in the aluminumalloy member. The thickness of the chill layer is set to 50 μm orgreater.

Furthermore, in the aspect of the invention, the metal member isconstituted by copper or a copper alloy, nickel or a nickel alloy, orsilver or a silver alloy.

According to the bonded body configured as described above, the chilllayer, in which a Si phase of which an aspect ratio (major axis/minoraxis) of a crystal grain is 2.5 or less and a crystal grain diameter is15 μm or less is dispersed, is formed on the bonding interface side withthe metal member in the aluminum alloy member, and the thickness of thechill layer is set to 50 μm or greater. Accordingly, it is possible toobstruct diffusion migration of a metal element that constitutes themetal member due to the chill layer, and thus occurrence of a Kirkendallvoid is suppressed. As a result, it is possible to lower heat resistancein a laminating direction.

According to another aspect of the invention, a power module substratewith heat sink is provided, including an insulating layer, a circuitlayer that is formed on one surface of the insulating layer, a metallayer that is formed on the other surface of the insulating layer, and aheat sink that is disposed on a surface, which is opposite to theinsulating layer, of the metal layer. In the metal layer, a bondingsurface with the heat sink is constituted by copper, nickel, or silver.In the heat sink, a bonding surface with the metal layer is constitutedby an aluminum alloy of which a solidus temperature is lower than aeutectic temperature of aluminum and a metal element that constitutesthe bonding surface of the metal layer. The heat sink and the metallayer are subjected to solid-phase diffusion bonding. A chill layer, inwhich a Si phase of which an aspect ratio of a crystal grain is 2.5 orless and a crystal grain diameter is 15 μm or less is dispersed, isformed on a bonding interface side with the metal layer in the heatsink. The thickness of the chill layer is set to 50 mm or greater.

According to the power module substrate with heat sink which isconfigured as described above, the chill layer, in which a Si phase ofwhich an aspect ratio (major axis/minor axis) of a crystal grain is 2.5or less and a crystal grain diameter is 15 μm or less is dispersed, isformed on the bonding interface side with the metal layer in the heatsink, and the thickness of the chill layer is set to 50 μm or greater.Accordingly, it is possible to obstruct diffusion migration of a metalelement that constitutes the metal layer due to the chill layer, andthus occurrence of a Kirkendall void is suppressed. As a result, heatresistance is low and heat dissipation characteristics are particularlyexcellent.

According to still another aspect of the invention, a heat sink isprovided, including a heat sink main body, and a metal member layer. Themetal member layer is formed from copper, nickel, or silver. The heatsink main body is constituted by an aluminum alloy of which a solidustemperature is lower than a eutectic temperature of aluminum and a metalelement that constitutes the metal member layer. A chill layer, in whicha Si phase of which an aspect ratio of a crystal grain is 2.5 or lessand a crystal grain diameter is 15 μm or less is dispersed, is formed ona bonding interface side with the metal member layer in the heat sinkmain body. The thickness of the chill layer is set to 50 μm or greater.

According to the heat sink configured as described above, the chilllayer, in which a Si phase of which an aspect ratio (major axis/minoraxis) of a crystal grain is 2.5 or less and a crystal grain diameter is15 μm or less is dispersed, is formed on the bonding interface side withthe metal member layer in the heat sink main body, and the thickness ofthe chill layer is set to 50 μm or greater. Accordingly, it is possibleto obstruct diffusion migration of a metal element that constitutes themetal member layer due to the chill layer, and thus occurrence of aKirkendall void is suppressed. As a result, heat resistance is low andheat dissipation characteristics are particularly excellent.

According to still another aspect of the invention, a method is providedof manufacturing a bonded body that is formed by bonding a metal memberformed from copper, nickel, or silver, and an aluminum alloy memberformed from an aluminum alloy of which a solidus temperature is lowerthan a eutectic temperature of aluminum and a metal element thatconstitutes the metal member. A chill layer, in which a Si phase ofwhich an aspect ratio of a crystal grain is 2.5 or less and a crystalgrain diameter is 15 μm or less is dispersed, is formed on a bondingsurface side with the metal member in the aluminum alloy member beforebonding, and the thickness of the chill layer is set to 80 μm orgreater. The aluminum alloy member and the metal member are subjected tosolid-phase diffusion bonding.

According to the method of manufacturing a bonded body which isconfigured as described above, the chill layer, in which a Si phase ofwhich an aspect ratio of a crystal grain is 2.5 or less and a crystalgrain diameter is 15 μm or less is dispersed, is formed on a bondingsurface side with the metal member in the aluminum alloy member beforebonding, and the thickness of the chill layer is set to 80 μm orgreater. Accordingly, it is possible to suppress diffusion migration ofa metal element, which constitutes the metal member, more than necessaryduring the solid-phase diffusion bonding, and thus it is possible tosuppress occurrence of a Kirkendall void.

Furthermore, a metal element, which constitutes the metal member, maydiffuse to a part of the chill layer during the solid-phase diffusionbonding in accordance with the metal element that constitutes the metalmember, and a diffusion bonding layer may be formed. Accordingly, thethickness of the chill layer after bonding may be smaller than thethickness of the chill layer before bonding.

Here, in the method of manufacturing a bonded body according to theaspect of the invention, it is preferable that the aluminum alloy memberand the metal member be laminated and electrically heated while beingpressurized in a laminating direction to subject the aluminum alloymember and the metal member to the solid-phase diffusion bonding.

In this case, since the aluminum alloy member and the metal member areelectrically heated while being pressurized in the laminating direction,it is possible to raise a temperature-rising rate, and thus it ispossible to perform the solid-phase diffusion bonding in relativelyshort time. According to this, for example, even when bonding isperformed in the atmosphere, an effect of oxidization on the bondingsurface is small, and thus it is possible to bond the aluminum alloymember and the metal member in a satisfactory manner.

According to still another aspect of the invention, a method is providedof manufacturing a power module substrate with heat sink which includesan insulating layer, a circuit layer that is formed on one surface ofthe insulating layer, a metal layer that is formed on the other surfaceof the insulating layer, and a heat sink that is disposed on a surface,which is opposite to the insulating layer, of the metal layer. In themetal layer, a bonding surface with the heat sink is constituted bycopper, nickel, or silver. In the heat sink, a bonding surface with themetal layer is constituted by an aluminum alloy of which a solidustemperature is lower than a eutectic temperature of aluminum and a metalelement that constitutes the bonding surface of the metal layer. A chilllayer, in which a Si phase of which an aspect ratio of a crystal grainis 2.5 or less and a crystal grain diameter is 15 μm or less isdispersed, is formed on a bonding surface side with the metal layer inthe heat sink before bonding, and the thickness of the chill layer isset to 80 μm or greater. The heat sink and the metal layer are subjectedto solid-phase diffusion bonding.

According to the method of manufacturing a power module substrate withheat sink which is configured as described above, the chill layer, inwhich a Si phase of which an aspect ratio of a crystal grain is 2.5 orless and a crystal grain diameter is 15 μm or less is dispersed, isformed on a bonding surface side with the metal layer in the heat sinkbefore bonding, and the thickness of the chill layer is set to 80 μm orgreater. Accordingly, it is possible to suppress diffusion migration ofa metal element, which constitutes the bonding surface of the metallayer, more than necessary during the solid-phase diffusion bonding, andthus it is possible to suppress occurrence of a Kirkendall void.

As a result, it is possible to manufacture a power module substrate withheat sink in which heat resistance in the laminating direction is lowand heat dissipation characteristics are excellent.

Here, in the method of manufacturing a power module substrate with heatsink according to the aspect of the invention, it is preferable that theheat sink and the metal layer be laminated and electrically heated whilebeing pressurized in a laminating direction to subject the heat sink andthe metal layer to the solid-phase diffusion bonding.

In this case, since the heat sink and the metal layer are electricallyheated while being pressurized in the laminating direction, it ispossible to raise a temperature-rising rate, and thus it is possible toperform the solid-phase diffusion bonding in relatively short time.According to this, for example, even when bonding is performed in theatmosphere, an effect of oxidization on the bonding surface is small,and thus it is possible to bond the heat sink and the metal layer in asatisfactory manner.

According to still another aspect of the invention, a method is providedof manufacturing a heat sink including a heat sink main body and a metalmember layer. The metal member layer is formed from copper, nickel, orsilver. The heat sink main body is constituted by an aluminum alloy ofwhich a solidus temperature is lower than a eutectic temperature ofaluminum and a metal element that constitutes the metal member layer. Achill layer, in which a Si phase of which an aspect ratio of a crystalgrain is 2.5 or less and a crystal grain diameter is 15 μm or less isdispersed, is formed on a bonding surface side with the metal memberlayer in the heat sink main body before bonding, and the thickness ofthe chill layer is set to 80 μm or greater. The heat sink main body andthe metal member layer are subjected to solid-phase diffusion bonding.

According to the method of manufacturing a heat sink which is configuredas described, since the chill layer, in which a Si phase of which anaspect ratio of a crystal grain is 2.5 or less and a crystal graindiameter is 15 μm or less is dispersed, is formed on the bonding surfaceside with the metal member layer in the heat sink main body beforebonding, and the thickness of the chill layer is set to 80 μm orgreater, it is possible to suppress diffusion migration of a metalelement, which constitutes the metal member layer, more than necessaryduring the solid-phase diffusion bonding, and thus it is possible tosuppress occurrence of a Kirkendall void.

As a result, it is possible to manufacture a heat sink in which heatresistance in the laminating direction is low and heat dissipationcharacteristics are excellent.

Here, in the method of manufacturing a heat sink according to the aspectof the invention, it is preferable that the heat sink main body and themetal member layer be laminated, and be electrically heated while beingpressurized in a laminating direction to subject the heat sink main bodyand the metal member layer to the solid-phase diffusion bonding.

In this case, since the heat sink main body and the metal member layerare electrically heated while being pressurized in the laminatingdirection, it is possible to raise a temperature-rising rate, and thusit is possible to perform the solid-phase diffusion bonding inrelatively short time. According to this, for example, even when bondingis performed in the atmosphere, an effect of oxidization on the bondingsurface is small, and thus it is possible to bond the heat sink mainbody and the metal member layer in a satisfactory manner.

Advantageous Effects of Invention

According to the aspects of the invention, it is possible to provide abonded body in which an aluminum alloy member formed from an aluminumalloy having a relatively low solidus temperature, and a metal memberformed from copper, nickel, or silver are bonded to each other in asatisfactory manner, and heat resistance in a laminating direction islow, a power module substrate with heat sink and a heat sink whichinclude the bonded body, a method of manufacturing a bonded body, and amethod of manufacturing a power module substrate with heat sink, and amethod of manufacturing a heat sink.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a power module including a powermodule substrate with heat sink according to a first embodiment of theinvention.

FIG. 2 is an enlarged cross-sectional view illustrating a bondinginterface between a heat sink and a metal layer (Cu layer) of the powermodule substrate with heat sink as illustrated in FIG. 1.

FIG. 3 is a flowchart illustrating a method of manufacturing the powermodule substrate with heat sink according to the first embodiment.

FIG. 4 is a schematic view illustrating the method of manufacturing thepower module substrate with heat sink according to the first embodiment.

FIG. 5 is an enlarged cross-sectional view illustrating a bondingsurface portion of a heat sink before bonding in the method ofmanufacturing the power module substrate with heat sink as illustratedin FIG. 4.

FIG. 6 is a schematic view illustrating a heat sink according to asecond embodiment of the invention.

FIG. 7 is an enlarged cross-sectional view illustrating a bondinginterface between a heat sink main body and a metal member layer of theheat sink illustrated in FIG. 6.

FIG. 8 is a flowchart illustrating a method of manufacturing the heatsink according to the second embodiment.

FIG. 9 is a schematic view illustrating the method of manufacturing theheat sink according to the second embodiment.

FIG. 10 is a schematic view illustrating a power module including apower module substrate with heat sink according to another embodiment ofthe invention.

FIG. 11 is a schematic view illustrating a situation in whichsolid-phase diffusion bonding is performed by an electrical heatingmethod.

FIG. 12 is a view illustrating a procedure of extracting a contour of aSi phase in examples.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, description will be given of embodiments of the inventionwith reference to the accompanying drawings.

FIG. 1 illustrates a power module 1 using a power module substrate withheat sink 30 according to a first embodiment of the invention.

The power module 1 includes the power module substrate with heat sink30, and a semiconductor element 3 that is bonded to one surface (anupper surface in FIG. 1) of the power module substrate with heat sink 30through a solder layer 2.

The power module substrate with heat sink 30 includes a power modulesubstrate 10 and a heat sink 31 that is bonded to the power modulesubstrate 10.

The power module substrate 10 includes a ceramic substrate 11 thatconstitutes an insulating layer, a circuit layer 12 that is arranged onone surface (an upper surface in FIG. 1) of the ceramic substrate 11,and a metal layer 13 that is arranged on the other surface of theceramic substrate 11.

The ceramic substrate 11 is constituted by ceramics such as siliconnitride (Si₃N₄), aluminum nitride (AlN), and alumina (Al₂O₃), which areexcellent in insulating properties and heat dissipation. In thisembodiment, the ceramic member 11 is constituted by the aluminum nitride(AlN), which is particularly excellent in heat dissipation. In addition,for example, the thickness of the ceramic substrate 11 is set in a rangeof 0.2 mm to 1.5 mm, and is set to 0.635 mm in this embodiment.

As illustrated in FIG. 4, the circuit layer 12 is formed by bonding analuminum plate 22, which is formed from aluminum or an aluminum alloy,onto one surface of the ceramic substrate 11. In this embodiment, thecircuit layer 12 is formed by bonding a rolled plate (aluminum plate 22)of aluminum (2N aluminum) having the purity of 99 mass % or greater tothe ceramic substrate 11. Furthermore, the thickness of the aluminumplate 22, which becomes the circuit layer 12, is set in a range of 0.1mm to 1.0 mm, and is set to 0.6 mm in this embodiment.

As illustrated in FIG. 1, the metal layer 13 includes an Al layer 13Athat is arranged on the other surface of the ceramic substrate 11, and aCu layer 13B that is laminated on a surface, which is opposite to asurface to which the ceramic substrate 11 is bonded, of the Al layer13A.

As illustrated in FIG. 4, the Al layer 13A is formed by bonding analuminum plate 23A, which is formed from aluminum or an aluminum alloy,onto the other surface of the ceramic substrate 11. In this embodiment,the Al layer 13A is formed by bonding a rolled plate (aluminum plate23A) of aluminum (2N aluminum) having the purity of 99 mass % or greaterto the ceramic substrate 11. The thickness of the aluminum plate 23Athat is bonded to the ceramic substrate 11 is set in a range of 0.1 mmto 3.0 mm, and is set to 0.6 mm in this embodiment.

As illustrated in FIG. 4, the Cu layer 13B is formed by bonding a copperplate 23B, which is formed from copper or a copper alloy, to the othersurface of the Al layer 13A. In this embodiment, the Cu layer 13B isformed by bonding a rolled plate (copper plate 23B) of oxygen-freecopper to the other surface of the Al layer 13A. The thickness of thecopper layer 13B is set in a range of 0.1 mm to 6 mm, and is set to 1 mmin this embodiment.

The heat sink 31 is configured to radiate heat on a power modulesubstrate 10 side. In this embodiment, as illustrated in FIG. 1, theheat sink 31 is provided with a flow passage 32 through which a coolingmedium flows. The heat sink 31 is constituted by a casted material of analuminum alloy of which a solidus temperature is lower than a eutectictemperature (548° C.) of Al and Cu which constitutes a bonding surface(Cu layer 13B) of the metal layer 13. Specifically, the heat sink 31 isconstituted by a casted material of ADC12 (solidus temperature: 515°C.), which is a Si-containing die-casting aluminum alloy defined in JISH 2118:2006. Furthermore, the ADC12 is an aluminum alloy that containsCu in a range of 1.5 mass % to 3.5 mass %, and Si in a range of 9.6 mass% to 12.0 mass %. In the casted material of the aluminum alloy, theamount of Si is preferably 1 mass % to 25 mass %, but there is nolimitation thereto.

As illustrated in FIG. 2, a chill layer 35 in which a Si phase of whichan aspect ratio (major axis/minor axis) of a crystal grain is 2.5 orless and a crystal grain diameter is 15 μm or less is dispersed, isformed on a bonding interface side with the metal layer 13 (Cu layer13B) in the heat sink 31. The aspect ratio (major axis/minor axis) of acrystal grain of the Si phase is preferably 1.0 to 2.0, and morepreferably 1.0 to 1.5. The crystal grain diameter is preferably 0.5 μmto 10 μm, and more preferably 1 μm to 7 μm. However, there is nolimitation to the ranges.

The chill layer 35 is formed in the vicinity of a surface layer portionof a casted material (portion in the vicinity of a casting mold) whenforming the casted material that constitutes the heat sink 31. In thechill layer 35, the crystal grain diameter is finer and the aspect ratiois smaller in comparison to the inside of the casted material.

The thickness of the chill layer 35 (thickness thereof after bonding) ofthe power module substrate with heat sink 30 is set to 50 μm or greater.The thickness of the chill layer 35 is preferably 100 μm or greater, andmore preferably 200 μm or greater, but there is no limitation to theranges.

Here, the heat sink 31 and the metal layer 13 (Cu layer 13B) aresubjected to solid-phase diffusion bonding.

As illustrated in FIG. 2, an intermetallic compound layer 38 is formedat a bonding interface between the metal layer 13 (Cu layer 13B) and theheat sink 31. That is, the intermetallic compound layer 38 is laminatedon the chill layer 35 of the heat sink 31.

The intermetallic compound layer 38 is formed through mutual diffusionof Al atoms of the heat sink 31 and Cu atoms of the Cu layer 13B. Theintermetallic compound layer 38 has a concentration gradient in whichthe concentration of Al atoms further decreases and the concentration ofCu atoms further increases as it goes toward the Cu layer 13B from theheat sink 31.

The intermetallic compound layer 38 is constituted by an intermetalliccompound composed of Cu and Al. In this embodiment, the intermetalliccompound layer 38 has a structure in which a plurality of theintermetallic compounds are laminated along the bonding interface. Here,the thickness of the intermetallic compound layer 38 is set in a rangeof 1 μm to 80 μm, and preferably in a range of 5 μm to 80 μm.

Furthermore, the intermetallic compound layer 38 is formed when Cu inthe Cu layer 13B diffuses to the heat sink 31 (chill layer 35) side, andSi particles contained in the heat sink 31 are dispersed in theintermetallic compound layer 38.

In this embodiment, the intermetallic compound layer 38 has a structurein which three kinds of intermetallic compounds are laminated. In theorder from the heat sink 31 side toward the Cu layer 13B side, a θ-phaseand a η₂-phase are laminated along the bonding interface between theheat sink 31 and the Cu layer 13B, and at least one phase among aζ₂-phase, a δ-phase, and a γ₂-phase is laminated.

In addition, at the bonding interface between the intermetallic compoundlayer and the Cu layer 13B, oxides are dispersed in a layer shape alongthe bonding interface. Furthermore, in this embodiment, the oxides arecomposed of aluminum oxides such as alumina (Al₂O₃). Furthermore, theoxides are dispersed at the interface between the intermetallic compoundlayer and the Cu layer 13B in a disconnected state, and a region inwhich the intermetallic compound layer and the Cu layer 13B are indirect contact with each other also exists. In addition, the oxides maybe dispersed at the inside of the θ-phase, the η₂-phase, or at least onephase among the ζ₂-phase, the δ-phase, and the γ₂-phase in a layershape.

Next, description will be given of a method of manufacturing the powermodule substrate with heat sink 30 according to this embodiment withreference to FIG. 3 to FIG. 5.

(Aluminum Plate-Laminating Process S01)

First, as illustrated in FIG. 4, the aluminum plate 22, which becomesthe circuit layer 12, is laminated on one surface of the ceramicsubstrate 11 through Al-Si-based brazing material foil 26.

In addition, the aluminum plate 23A, which becomes the Al layer 13A, islaminated on the other surface of the ceramic substrate 11 throughAl-Si-based brazing material foil 26. Furthermore, in this embodiment,as the Al-Si-based brazing material foil 26, Al-8 mass % Si alloy foilhaving a thickness of 10 μm is used.

(Circuit Layer- and Al Layer-Forming Process S02)

In addition, the resultant laminated body is disposed in a vacuumheating furnace and is heated therein in a pressurized state (pressureis set to 1 to 35 kgf/cm² (0.10 to 3.43 MPa)) in a laminating directionto bond the aluminum plate 22 and the ceramic substrate 11, therebyforming the circuit layer 12. In addition, the ceramic substrate 11 andthe aluminum plate 23A are bonded to form the Al layer 13A.

Here, it is preferable that the pressure inside the vacuum heatingfurnace be set in a range of 10⁻⁶ Pa to 10⁻³ Pa, a heating temperaturebe set to 600° C. to 650° C., and retention time be set in a range of 30minutes to 180 minutes.

(Cu Layer (Metal Layer)-Forming Process S03)

Next, the copper plate 23B, which becomes the Cu layer 13B, is laminatedon the other surface side of the Al layer 13A.

In addition, the resultant laminated body is disposed in a vacuumheating furnace and is heated therein in a pressurized state (pressureis set to 3 to 35 kgf/cm² (0.29 to 3.43 MPa)) in a laminating directionto subject the Al layer 13A and the copper plate 23B to solid-phasediffusion bonding, thereby forming the metal layer 13.

Here, it is preferable that the pressure inside the vacuum heatingfurnace be set in a range of 10⁻⁶ Pa to 10⁻³ Pa, a heating temperaturebe set to 400° C. to 548° C., and retention time be set in a range of 5minutes to 240 minutes.

Furthermore, in respective bonding surfaces, which are subjected to thesolid-phase diffusion bonding, of the Al layer 13A and the copper plate23B, scratches on the bonding surfaces are removed in advance and thusthe bonding surfaces are made to be smooth.

(Heat Sink-Preparing Process S04)

Next, the heat sink 31 to be bonded is prepared. At this time, asillustrated in FIG. 5, the chill layer 35A, in which a Si phase of whichan aspect ratio of a crystal grain is 2.5 or less and a crystal graindiameter is 15 μm or less is dispersed, is formed on a bonding surfaceside with the metal layer 13 (Cu layer 13B) in the heat sink 31, and thethickness of the chill layer 35A is set to 80 μm or greater. Thethickness of the chill layer 35A is preferably 100 μm or greater, andmore preferably 200 μm or greater, but there is no limitation to theranges.

Here, during casting of the heat sink 31, it is possible to control thethickness of the chill layer 35A by adjusting a cooling rate at least inthe vicinity of the bonding surface of the heat sink 31. In this case,for example, a temperature of a mold during the casting may be set to230° C. or lower, and preferably 210° C. or lower. The temperature ofthe mold during the casting may be set to 140° C. or higher, andpreferably 160° C. or higher.

In addition, as conditions during casting of the heat sink, for example,an injection pressure may be set to 400 kg/cm² to 600 kg/cm², a moltenmetal temperature may be set to 650° C. to 750° C., an injection speedmay be set to 30 m/s to 60 m/s, and a sleeve-filling rate may be set to40% to 60%. Examples of an atmosphere include an inert atmosphere suchas nitrogen and argon, an oxygen atmosphere, a vacuum atmosphere, andthe like.

In addition, the thickness of the chill layer 35A can be controlled byadjusting a grinding amount of a surface after casting.

(Metal Layer/Heat Sink-Bonding Process S05)

Next, the metal layer 13 (Cu layer 13B) and the heat sink 31 arelaminated, and the resultant laminated body is disposed in a vacuumheating furnace and is heated therein in a pressurized state (pressureis set to 5 to 35 kgf/cm² (0.49 to 3.43 MPa)) in a laminating directionto subject the metal layer 13 (Cu layer 13B) and the heat sink 31 tosolid-phase diffusion bonding. Furthermore, in respective bondingsurfaces, which are subjected to the solid-phase diffusion bonding, ofthe metal layer 13 (Cu layer 13B) and the heat sink 31, scratches on thebonding surface are removed in advance and thus the bonding surfaces aremade to be smooth. A pressure during the pressurization is preferablyset to 8 to 20 kgf/cm² (0.78 to 1.96 MPa), but there is no limitation tothis range.

Here, it is preferable that a pressure inside the vacuum heating furnacebe set in a range of 10⁻⁶ Pa to 10⁻³ Pa, a heating temperature be set ina range of 400° C. to 520° C., and retention time be set in a range of0.25 hours to 3 hours. It is more preferable that the pressure insidethe vacuum heating furnace be set in a range of 10⁻⁵ Pa to 10⁻⁴ Pa, theheating temperature be set in a range of 480° C. to 510° C., and theretention time be set in a range of 0.5 hours to 2 hours. However, thereis no limitation to the ranges.

In the metal layer/heat sink-bonding process S05, Cu atoms in the Culayer 13B diffuse to the chill layer 35A side of the heat sink 31, andthus the intermetallic compound layer 38 and the chill layer 35 areformed as illustrated in FIG. 2.

In this manner, the power module substrate with heat sink 30 accordingto this embodiment is manufactured.

(Die-Bonding Process S06)

Next, the semiconductor element 3 is laminated on one surface (frontsurface (upper side in FIG. 1)) of the circuit layer 12 through a soldermaterial 2, and the resultant laminated body is subjected to solderbonding in a reducing furnace.

As described above, the power module 1 according to this embodiment ismanufactured.

According to the power module substrate with heat sink 30 according tothis embodiment which is configured as described, the heat sink 31 isconstituted by an aluminum alloy of which a solidus temperature is lowerthan a eutectic temperature (548° C.) of Al and Cu that constitutes thebonding surface (Cu layer 13B) of the metal layer 13. Specifically, theheat sink 31 is constituted by a casted material of ADC12 (solidustemperature: 515° C.), which is a die-casting aluminum alloy defined inJIS H 2118:2006. Accordingly, it is possible to constitute the heat sink31 with a complicated structure including the flow passage 32, and thusit is possible to improve a heat dissipation performance.

In addition, in this embodiment, the chill layer 35, in which a Si phaseof which an aspect ratio (major axis/minor axis) of a crystal grain is2.5 or less and a crystal grain diameter is 15 μm or less is dispersed,is formed on the bonding interface side with the metal layer 13 (Culayer 13B) in the heat sink 31, and the thickness of the chill layer 35is set to 50 μm or greater. Accordingly, it is possible to obstructdiffusion migration of Cu atoms of the metal layer 13 (Cu layer 13B) dueto the chill layer 35, and thus it is possible to suppress occurrence ofa Kirkendall void. According to this, even in a case where the powermodule substrate with heat sink 30 is maintained at a high temperature,heat resistance in the laminating direction does not increase, and thusit is possible to suppress deterioration of heat dissipationcharacteristics.

In addition, in this embodiment, the intermetallic compound layer 38,which is constituted by an intermetallic compound layer of Cu and Al, isformed at the bonding interface between the metal layer 13 (Cu layer13B) and the heat sink 31. The intermetallic compound layer 38 has astructure in which a plurality of the intermetallic compounds arelaminated along the bonding interface, and thus it is possible tosuppress great growth of the intermetallic compounds which are brittle.In addition, a volume variation at the inside of the intermetalliccompound layer 38 decreases, and thus an internal strain is suppressed.

In addition, in this embodiment, at the bonding interface between the Culayer 13B and the intermetallic compound layer 38, oxides are dispersedin a layer shape along the bonding interface. Accordingly, an oxide filmformed on the bonding surface of the heat sink 31 is reliably broken,and mutual diffusion of Cu and Al sufficiently progresses, and thus theCu layer 13B and the heat sink 31 are reliably bonded to each other.

In addition, according to the method of manufacturing the power modulesubstrate with heat sink 30 according to this embodiment, in the heatsink 31 before bonding which is prepared in the heat sink-preparingprocess S04, the chill layer 35A, in which a Si phase of which an aspectratio of a crystal grain is 2.5 or less and a crystal grain diameter is15 μm or less is dispersed, is formed on the bonding surface side withthe metal layer 13 (Cu layer 13B) in the heat sink 31, and the thicknessof the chill layer 35A is set to 80 μm or greater. Accordingly, in themetal layer/heat sink-bonding process S05, when the heat sink 31 and themetal layer 13 (Cu layer 13B) are subjected to the solid-phase diffusionbonding, it is possible to suppress diffusion migration of Cu atoms ofthe Cu layer 13B more than necessary, and thus it is possible tosuppress occurrence of the Kirkendall void.

Accordingly, it is possible to manufacture the power module substratewith heat sink 30 in which heat resistance in the laminating directionis low and heat dissipation characteristics are excellent.

In addition, in a case where scratches exist on the bonding surfaceduring the solid-phase diffusion bonding, there is a concern that a gapmay occur in the bonding interface. However, in this embodiment, bondingsurfaces of the Cu layer 13B (copper plate 23B) and the heat sink 31 aremade to be flat by removing scratches on the bonding surface, and aresubjected to the solid-diffusion bonding, and thus it is possible tosuppress occurrence of a gap in the bonding interface. As a result, itis possible to reliably perform the solid-phase diffusion bonding.

Furthermore, typically, during grinding of the surface of the heat sink31 that is constituted by a casted material, a chill layer, which isformed in a surface layer in a small thickness, is removed. However, inthis embodiment, the chill layer is formed in a large thickness duringcasting, and thus the chill layer remains after the surface grinding.

In this embodiment, the upper limit of the thickness of the chill layeris not particularly limited, and in a case of using the heat sink 31constituted by a casted material, it is preferable to set the upperlimit to 5000 μm or less. In a case of manufacturing the heat sink 31through casting, it is difficult to manufacture the heat sink 31 inwhich the thickness of the chill layer is greater than 5000 μm.

In addition, in a case where the heat sink 31 is thin, the entirety ofthe heat sink 31 may be the chill layer. Even in this case, the sameoperational effect as in this embodiment can be exhibited.

Second Embodiment

Next, description will be given of a heat sink according to a secondembodiment of the invention. FIG. 6 illustrates a heat sink 101according to the second embodiment of the invention.

The heat sink 101 includes a heat sink main body 110, and a metal memberlayer 117 that is laminated on one surface (upper side in FIG. 6) of theheat sink main body 110 and is formed from copper, nickel, or silver. Inthis embodiment, as illustrated in FIG. 9, the metal member layer 117 isconstructed through bonding of a metal plate 127 that is constituted bya rolled plate of oxygen-free copper.

The heat sink main body 110 is provided with a flow passage 111 throughwhich a cooling medium flows. The heat sink main body 110 is constitutedby an aluminum alloy having a solidus temperature that is lower than aeutectic temperature (548° C.) of Al and a metal element (Cu in thisembodiment) that constitutes the metal member layer 117. Specifically,the heat sink main body 110 is constituted by a casted material of ADC14(solidus temperature: 507° C.), which is a Si-containing die-castingaluminum alloy defined in JIS H 2118:2006. Furthermore, ADC14 is analuminum alloy that contains Si in a range of 16 mass % to 18 mass %,and Mg in a range of 0.45 mass % to 0.65 mass %. In the aluminum alloy,the amount of Si is preferably 1 mass % to 25 mass %, but there is nolimitation thereto.

In addition, as illustrated in FIG. 7, a chill layer 135 in which a Siphase of which an aspect ratio (major axis/minor axis) of a crystalgrain is 2.5 or less and a crystal grain diameter is 15 μm or less isdispersed, is formed on a bonding interface side with the metal memberlayer 117 in the heat sink main body 110. The aspect ratio (majoraxis/minor axis) of a crystal grain of the Si phase is preferably 1.0 to2.0, and more preferably 1.0 to 1.5. The crystal grain diameter ispreferably 0.5 μm to 10 μm, and more preferably 1 μm to 7 μm. However,there is no limitation to the ranges.

The chill layer 135 is formed in the vicinity of a surface layer portionof a casted material (portion in the vicinity of a casting mold) whenforming the casted material that constitutes the heat sink main body110. In the chill layer 135, the crystal grain diameter is finer and theaspect ratio is smaller in comparison to the inside of the castedmaterial.

The thickness of the chill layer 135 is set to 50 μm or greater. Thethickness of the chill layer 135 is preferably 100 μm or greater, andmore preferably 200 μm or greater, but there is no limitation to theranges.

Here, the heat sink main body 110 and the metal member layer 117 aresubjected to the solid-phase diffusion bonding.

As illustrated in FIG. 7, an intermetallic compound layer 138 is formedat a bonding interface between the heat sink main body 110 and the metalmember layer 117. The intermetallic compound layer 138 is formed throughmutual diffusion of Al atoms of the heat sink main body 110 and Cu atomsof the metal member layer 117. The intermetallic compound layer 138 hasa concentration gradient in which the concentration of Al atoms furtherdecreases and the concentration of Cu atoms further increases as it goestoward the metal member layer 117 from the heat sink main body 110.

The intermetallic compound layer 138 is constituted by an intermetalliccompound composed of Cu and Al. In this embodiment, the intermetalliccompound layer 138 has a structure in which a plurality of theintermetallic compounds are laminated along the bonding interface. Here,the thickness of the intermetallic compound layer 138 is set in a rangeof 1 μm to 80 μm, and preferably in a range of 5 μm to 80 μm.

Furthermore, the intermetallic compound layer 138 is formed when Cu inthe metal member layer 117 diffuses to the heat sink main body 110(chill layer 135) side, and Mg particles contained in the heat sink mainbody 110 may be dispersed in the intermetallic compound layer 138.

In this embodiment, the intermetallic compound layer 138 has a structurein which three kinds of intermetallic compounds are laminated. In theorder from the heat sink main body 110 side toward the metal memberlayer 117 side, a θ-phase and a η₂-phase are laminated along the bondinginterface between the heat sink main body 110 and the metal member layer117, and at least one phase among a ζ₂-phase, a δ-phase, and a γ₂-phaseis laminated.

In addition, at the bonding interface between the intermetallic compoundlayer 138 and the metal member layer 117, oxides are dispersed in alayer shape along the bonding interface. Furthermore, in thisembodiment, the oxides are composed of aluminum oxides such as alumina(Al₂O₃). Furthermore, the oxides are dispersed at the interface betweenthe intermetallic compound layer 138 and the metal member layer 117 in adisconnected state, and a region in which the intermetallic compoundlayer 138 and the metal member layer 117 are in direct contact with eachother also exists. In addition, the oxides may be dispersed at theinside of the θ-phase, the η₂₋phase, or at least one phase among theζ₂-phase, the δ-phase, and the γ₂-phase in a layer shape.

Next, description will be given of a method of manufacturing the heatsink 101 according to this embodiment with reference to FIG. 8 and FIG.9.

(Heat Sink Main Body-Preparing Process S101)

First, the heat sink main body 110 to be bonded is prepared. At thistime, as is the case with the heat sink 31 (refer to FIG. 5) describedin the first embodiment, the chill layer, in which a Si phase of whichan aspect ratio of a crystal grain is 2.5 or less and a crystal graindiameter is 15 μm or less is dispersed, is formed on a bonding surfaceside with the metal member layer 117 in the heat sink main body 110, andthe thickness of the chill layer is set to 80 μm or greater. Thethickness of the chill layer is preferably 100 μm or greater, and morepreferably 200 μm or greater, but there is no limitation to the ranges.

Here, during casting of the heat sink main body 110, it is possible tocontrol the thickness of the chill layer by adjusting a cooling rate atleast in the vicinity of the bonding surface of the heat sink main body110. In this case, for example, a temperature of a mold during thecasting may be set to 230° C. or lower, and preferably 210° C. or lower.The temperature of the mold during the casting may be set to 140° C. orhigher, and preferably 160° C. or higher. In addition, as conditionsduring casting of the heat sink main body 110, for example, an injectionpressure may be set to 400 kg/cm² to 600 kg/cm², a molten metaltemperature may be set to 650° C. to 750° C., an injection speed may beset to 30 m/s to 60 m/s, and a sleeve-filling rate may be set to 40% to60%. Examples of an atmosphere include an inert atmosphere such asnitrogen and argon, an oxygen atmosphere, a vacuum atmosphere, and thelike.

In addition, the thickness of the chill layer can be controlled byadjusting a grinding amount of a surface after casting.

(Heat Sink Main Body/Metal Member Layer-Bonding Process S102)

Next, as illustrated in FIG. 9, the heat sink main body 110 and themetal plate 127 that becomes the metal member layer 117 are laminated,and the resultant laminated body is disposed in a vacuum heating furnaceand is heated therein in a pressurized state (pressure is set to 1 to 35kgf/cm² (0.10 to 3.43 MPa)) in a laminating direction to subject themetal plate 127 and the heat sink main body 110 to solid-phase diffusionbonding. Furthermore, in respective bonding surfaces, which aresubjected to the solid-phase diffusion bonding, of the metal plate 127and the heat sink main body 110, scratches on the bonding surface areremoved in advance and thus the bonding surfaces are made to be smooth.A pressure during the pressurization is preferably set to 8 to 20kgf/cm² (0.78 to 1.96 MPa), but there is no limitation to this range.

Here, it is preferable that a pressure inside the vacuum heating furnacebe set in a range of 10⁻⁶ Pa to 10⁻³ Pa, a heating temperature be set ina range of 400° C. to 520° C., and retention time be set in a range of0.25 hours to 3 hours. It is more preferable that the pressure insidethe vacuum heating furnace be set in a range of 10⁻⁵ Pa to 10⁻⁴Pa, theheating temperature be set in a range of 480° C. to 510° C., and theretention time be set in a range of 0.5 hours to 2 hours. However, thereis no limitation to the ranges.

In the heat sink main body/metal member layer-bonding process S102, Cuatoms in the metal plate 127 diffuse to the chill layer side of the heatsink main body 110, and thus the intermetallic compound layer 138 andthe chill layer 135 are formed as illustrated in FIG. 7.

In this manner, the heat sink 101 according to this embodiment ismanufactured.

According to the heat sink 101 according to this embodiment which isconfigured as described above, the metal member layer 117 is formed bybonding the metal plate 127 constituted by a rolled plate of oxygen-freecopper on one surface side of the heat sink main body 110, and thus itis possible to make heat spread in a plane direction by the metal memberlayer 117, and thus it is possible to greatly improve heat dissipationcharacteristics. In addition, it is possible to bond another member andthe heat sink 101 by using solder and the like in a satisfactory manner.

In addition, the heat sink main body 110 is constituted by an aluminumalloy having the solidus temperature that is lower than the eutectictemperature (548° C.) of Al and the metal element (Cu) that constitutesthe metal member layer 117. Specifically, the heat sink main body 110 isconstituted by a casted material of ADC14 (solidus temperature: 507°C.), which is a die-casting aluminum alloy defined in JIS H 2118:2006.Accordingly, it is possible to construct the heat sink main body 110with a complicated structure including a flow passage and the like.

In addition, in this embodiment, the chill layer 135, in which a Siphase of which an aspect ratio (major axis/minor axis) of a crystalgrain is 2.5 or less and a crystal grain diameter is 15 μm or less isdispersed, is formed on a bonding interface side with the metal memberlayer 117 in the heat sink main body 110, and the thickness of the chilllayer 135 is set to 50 μm or greater. Accordingly, it is possible toobstruct diffusion migration of Cu atoms of the metal member layer 117due to the chill layer 135, and thus it is possible to suppressoccurrence of the Kirkendall void. According to this, even in a casewhere the heat sink 101 is maintained at a high temperature, heatresistance in the laminating direction does not increase, and thus it ispossible to suppress deterioration of heat dissipation characteristics.

In addition, in this embodiment, the bonding interface between the metalmember layer 117 and the heat sink main body 110 has the sameconfiguration as the bonding interface between the Cu layer 13B and theheat sink 31 in the first embodiment, and thus it is possible to exhibitthe same operational effect as in the first embodiment.

In this embodiment, the upper limit of the thickness of the chill layeris not particularly limited, and in a case of using the heat sink mainbody 110 constituted by a casted material, it is preferable to set theupper limit to 5000 μm or less. In a case of manufacturing the heat sinkmain body 110 through casting, it is difficult to manufacture the heatsink main body 110 in which the thickness of the chill layer is greaterthan 5000 μm.

In addition, in a case where the heat sink main body 110 is thin, theentirety of the heat sink main body 110 may be the chill layer. Even inthis case, the same operational effect as in this embodiment can beexhibited.

Hereinbefore, description has been given of the embodiments of theinvention. However, the invention is not limited thereto, andmodifications can be appropriately made in a range not departing fromthe technical spirit of the invention.

For example, in the embodiments, description has been given of a casewhere the Cu layer formed from copper as the metal member layer issubjected to bonding. However, a Ni layer formed from nickel or a nickelalloy or a Ag layer formed from silver or a silver alloy may besubjected to the bonding instead of the Cu layer.

In a case of forming the Ni layer instead of the Cu layer, solderabilitybecomes satisfactory, and thus it is possible to improve bondingreliability with another member. In addition, in a case of forming theNi layer through the solid-phase diffusion bonding, it is not necessaryto perform a masking treatment that is performed when forming a Niplating film through electroless plating and the like, and thus it ispossible to reduce the manufacturing cost. In this case, it ispreferable that the thickness of the Ni layer be set to 1 μm to 30 μm.In a case where the thickness of the Ni layer is less than 1 μm, thereis a concern that the effect of improving the bonding reliability withanother member may disappear, and in a case where the thickness isgreater than 30 μm, there is a concern that the Ni layer becomes a heatresistant body and thus it is difficult to efficiently transfer heat. Inaddition, in a case of forming the Ni layer through the solid-phasediffusion bonding, with regard to solid-phase diffusion bonding betweenan Al layer and Ni, a bonding temperature is set to 400° C. to 520° C.,but the other conditions can be set to the same conditions as in theabove-described embodiments.

In a case of forming the Ag layer instead of the Cu layer, for example,when bonding the Ag layer with another member by using a silver oxidepaste including silver oxide particles and a reducing agent composed ofan organic material, bonding between silver after a silver oxide of thesilver oxide paste is reduced by the reducing agent, and the Ag layer isbonded between the same kinds of metals, and thus it is possible toimprove the bonding reliability. In addition, the Ag layer havingsatisfactory heat conductivity is formed, and thus it is possible toefficiently and widely transfer heat in an in-plane direction. In thiscase, it is preferable that the thickness of the Ag layer be set to 1 mmto 20 μm. In a case where the thickness of the Ag layer is less than 1μm, there is a concern that the effect of improving the bondingreliability with another member may disappear, and in a case where thethickness is greater than 20 μm, there is a concern that the effect ofimproving the bonding reliability is not obtained and an increase in thecost is caused. In addition, in a case of forming the Ag layer throughthe solid-phase diffusion bonding, as a solid-phase diffusion bondingcondition between an Al layer and Ag, a bonding temperature is set to400° C. to 520° C., but the other conditions can be set to the sameconditions as in the above-described embodiments.

In addition, in the first embodiment, description has been given of aconfiguration in which the metal layer 13 includes the Al layer 13A andthe Cu layer 13B, but there is no limitation thereto. As illustrated inFIG. 10, the entirety of the metal layer may be constituted by copper ora copper alloy. In a power module substrate with heat sink 230illustrated in FIG. 10, a copper plate is bonded to a surface on theother side (lower side in FIG. 10) of the ceramic substrate 11 inaccordance with a DBC method, an active metal brazing method, and thelike, and a metal layer 213 formed from copper or a copper alloy isformed. In addition, the metal layer 213 and the heat sink 31 aresubjected to the solid-phase diffusion bonding. Furthermore, in thepower module substrate 210 illustrated in FIG. 10, a circuit layer 212is also constituted by copper or a copper alloy. A power module 201illustrated in FIG. 10 includes the power module substrate with heatsink 230, and a semiconductor element 3 that is bonded to one surface(upper surface in FIG. 10) of the power module substrate with heat sink230 through a solder layer 2.

In the first embodiment, description has been given of a configurationin which the circuit layer is formed through bonding of an aluminumplate having the purity of 99 mass %, but there is no limitationthereto. The circuit layer may be constituted by other metals such aspure aluminum having the purity of 99.99 mass % or greater, anotheraluminum or an aluminum alloy, and copper or a copper alloy. Inaddition, the circuit layer may be set to have a two-layer structure ofan Al layer and a Cu layer. This is also true of the power modulesubstrate 210 illustrated in FIG. 10.

In the metal layer/heat sink-bonding process S05 according to the firstembodiment, description has been given of a configuration in which themetal layer 13 (Cu layer 13B) and the heat sink 31 are laminated, andthe resultant laminated body is disposed in a vacuum heating furnace andis heated therein in a pressurized state in a laminating direction. Inaddition, in the heat sink main body/metal member layer-bonding process5102 according to the second embodiment, description has been given of aconfiguration in which the heat sink main body 110 and the metal plate127 that becomes the metal member layer 117 are laminated, and theresultant laminated body is disposed in a vacuum heating furnace and isheated therein in a pressurized state (pressure of 5 to 35 kgf/cm²)(0.49 to 3.43 MPa)) in a laminating direction. However, there is nolimitation to the above-described configurations, and as illustrated inFIG. 11, an electrical heating method may be applied when subjecting analuminum alloy member 301 (the heat sink 31 or the heat sink main body110), and a metal member 302 (the metal layer 13 or the metal memberlayer 117) to the solid-phase diffusion bonding.

In a case of performing the electrical heating, as illustrated in FIG.11, the aluminum alloy member 301 and the metal member 302 arelaminated, and the resultant laminated body is pressurized in alaminating direction by a pair of electrodes 312 and 312 through carbonplates 311 and 311, and electrification is performed with respect to thealuminum alloy member 301 and the metal member 302. In this case, thecarbon plates 311 and 311, the aluminum alloy member 301, and the metalmember 302 are heated by Joule's heat, and thus the aluminum alloymember 301 and the metal member 302 are subjected to the solid-phasediffusion bonding.

In the above-described electrical heating method, the aluminum alloymember 301 and the metal member 302 are directly electrically heated.Accordingly, for example, it is possible to make a temperature risingrate be as relatively fast as 30 to 100° C./min, and thus it is possibleto perform the solid-phase diffusion bonding in a short time. As aresult, an influence of oxidation on a bonding surface is small, andthus it is also possible to perform bonding, for example, in anatmospheric atmosphere. In addition, in accordance with a resistancevalue or specific heat of the aluminum alloy member 301 and the metalmember 302, it is possible to bond the aluminum alloy member 301 and themetal member 302 in a state in which a temperature difference occurstherebetween, and thus a difference in thermal expansion decreases. As aresult, it is possible to realize a reduction in thermal stress.

Here, in the above-described electrical heating method, it is preferablethat a pressurizing load applied by the pair of electrodes 312 and 312be set in a range of 30 kgf/cm² to 100 kgf/cm² (2.94 MPa to 9.81 MPa).The pressurizing load is more preferably set in a range of 50 kgf/cm² to80 kgf/cm² (4.90 MPa to 7.85 MPa), but there is no limitation to theranges.

In addition, in a case of applying the electrical heating method, withregard to surface roughness of the aluminum alloy member 301 and themetal member 302, it is preferable that arithmetic average roughness Rabe set to 0.3 μm to 0.6 μm, and the maximum height Rz be set in a rangeof 1.3 μm to 2.3 μm. In typical solid-phase diffusion bonding, it ispreferable that the surface roughness of the bonding surface be small.However, in a case of the electrical heating method, when the surfaceroughness of the bonding surface is too small, interface contactresistance decreases, and thus it is difficult to locally heat thebonding interface. Accordingly, the surface roughness is preferably setin the above-described range.

Furthermore, the above-described electrical heating method can be usedin the metal layer/heat sink-bonding process S05 according to the firstembodiment. In this case, since the ceramic substrate 11 is aninsulator, thus it is necessary to short-circuit the carbon plates 311and 311, for example, with a jig formed from carbon, and the like.Bonding conditions are the same as those in the bonding between thealuminum member 301 and the copper member 302.

In addition, surface roughness of the metal layer 13 (Cu layer 13B) andthe heat sink 31 is the same as in the case of the aluminum member 301and the copper member 302.

EXAMPLES

Hereinafter, description will be given of results of a confirmationexperiment that is performed to confirm the effect of the invention.

(Preparation of Test Piece)

One surface of an aluminum alloy plate (50 mm×50 mm, thickness: 5 mm)illustrated in Table 1 was ground until reaching the thickness of achill layer in Table 1, and a metal plate (40 mm×40 mm, thicknessillustrated in Table 1) illustrated in Table 1 was solid-phasediffusion-bonded to the surface in accordance with the method describedin the embodiments.

In Examples 1 to 5, and Comparative Examples 1 to 3, the aluminum alloyplate and the metal plate were subjected to solid-phase diffusionbonding under conditions of 500° C. and 180 minutes with a vacuumheating furnace while being pressurized in a laminating direction with aload of 15 kgf/cm² (1.47 MPa).

In Examples 6 to 10, the aluminum alloy plate and the metal plate weresubjected to the solid-phase diffusion bonding in accordance with theelectrical heating method illustrated in FIG. 11. Furthermore, apressurizing load with the electrodes was set to 15 kgf/cm² (1.47 MPa),a heating temperature (copper plate temperature) was set to 510° C.,retention time at the heating temperature was set to 5 minutes, and atemperature rising rate was set to 80° C./minute. In addition, a bondingatmosphere was set to an atmospheric atmosphere.

(Thickness of Chill Layer in Aluminum Alloy Plate before Bonding)

The aluminum plate was observed before bonding, and the thickness of thechill layer formed on the bonding surface side was measured as follows.

First, surface analysis of Si was performed with respect to the surfaceof the aluminum plate by using EPMA (JXA-8530F, manufactured by JEOLLtd.) under conditions of a visual field of 360 μm square, anacceleration voltage of 15 kV, and a Si contour level of 0 to 1000,thereby obtaining a Si distribution image illustrated in FIG. 12(a).

The Si distribution image obtained was converted into an 8-bit grayscale, thereby obtaining a Si distribution image illustrated in FIG.12(b).

Next, the Si distribution image was binarized as illustrated in FIG.12(c) on the basis of Kapur-Sahoo-Wong (Maximum Entropy) thresholdingmethod (Kapur, JN; Sahoo, PK; Wong, ACK(1985), “A New Method forGray-level Picture Thresholding Using the Entropy of the Histogram”,Graphical Models and Image Processing 29(3): refer to 273-285).

Next, as illustrated in FIG. 12(d), the contour of the Si phase wasextracted from the binarized image through elliptic approximation.

An aspect ratio and a crystal grain diameter were calculated from thefollowing expression by using a major axis and a minor axis which wereobtained from the elliptic approximation on the basis of the image fromwhich the contour of the Si phase was extracted.

Aspect ratio=major axis/minor axis

Crystal grain diameter=major axis

In addition, in an area of 360 μm², the number of particles satisfyingconditions in which the aspect ratio is 2.5 or less and the crystalgrain diameter is 15 μm or less (hereinafter, simply referred to as“conditions”) and the number of particles not satisfying were obtainedto obtain a ratio of the number of particles satisfying theconditions/the number of particles not satisfying the condition.

Measurement was performed for every 10 μm from a surface of the aluminumplate toward the inside of the plate in accordance with the measurementmethod, and a portion in which the ratio of the number of particlessatisfying the conditions/the number of particles not satisfying theconditions is three or greater was defined as a chill layer, and thethickness of the chill layer was obtained.

Evaluation results are illustrated in Table 1.

(Thickness of Chill Layer at Bonding Interface Between Aluminum AlloyPlate and Metal Plate After Bonding)

A cross-sectional observation of a bonded body of the aluminum alloyplate and the metal plate, which were subjected to the solid-phasediffusion bonding, was performed and the thickness of the chill layerformed at the bonding interface was measured as follows.

The bonding interface of the bonded body was observed by using EPMA(JXA-8530F, manufactured by JEOL Ltd.) to obtain the thickness of anintermetallic compound of Al that grows to the inside of the aluminumalloy plate and a metal element (Cu, Ni, Ag) of the metal plate. Athickness, which was obtained by subtracting the thickness of theintermetallic compound of Al and the metal element (Cu, Ni, Ag) of themetal plate from the thickness of the chill layer before bonding, wasset as the thickness of the chill layer after bonding.

Furthermore, the thickness of the intermetallic compound was measured asfollows. Line analysis of the bonding interface was performed in athickness direction of the bonded body. A region in which theconcentration of Al was 65 at % to 70 at % was regarded as theintermetallic compound in a case of using copper as the metal plate, aregion in which the concentration of Al was 55 at % to 80 at % wasregarded as the intermetallic compound in a case of using nickel as themetal plate, and a region in which the concentration of Al was 20 at %to 45 at % was regarded as the intermetallic compound in a case of usingsilver as the metal plate. Then, the thickness of the region wasmeasured as the thickness of the intermetallic compound.

Evaluation results are illustrated in Table 1.

(Heat Cycle Test)

Next, a heat cycle test was performed with respect to the bonded bodythat was manufactured as described above. The heat cycle for 5 minutesat −40° C. and for 5 minutes at 150° C. was applied to the test piece(power module with heat sink) 4000 times by using a thermal impacttester (TSB-51, manufactured by ESPEC CORP.) in a liquid phase(Fluorinert).

In addition, heat resistance in the laminating direction of the bondedbody before the heat cycle test, and heat resistance in the laminatingdirection of the bonded body after the heat cycle test were evaluated asfollows.

(Measurement of Heat Resistance)

A heater chip (13 mm×10 mm×0.25 mm) was soldered to a surface of themetal plate, and the aluminum alloy plate was brazed to a coolingdevice. Next, the heater chip was heated at power of 100 W, and atemperature of the heater chip was measured by using a thermocouple. Inaddition, a temperature of a cooling medium (ethylene glycol:water=9:1),which flows through the cooling device, was measured. In addition, avalue obtained by dividing a difference between the temperature of theheater chip and the temperature of the cooling medium by electric powerwas set as heat resistance.

Furthermore, heat resistance in Comparative Example 1, in which thealuminum alloy plate and the copper plate were subjected to thesolid-phase diffusion bonding without forming the chill layer, beforethe heat cycle was set to “1” as a reference, and the heat resistancewas evaluated as a ratio with Comparative Example 1. Evaluation resultsare illustrated in Table 1.

TABLE 1 Metal plate Aluminum alloy plate Thickness of chill layer Heatresistance Thickness Solidus Before After Before After Material (μm)Material temperature (° C.) bonding (μm) bonding (μm) heat cycle heatcycle Example 1 Oxygen-free copper 1500 AC4B 520 550 530 0.940 0.959Example 2 Oxygen-free copper 1500 AC9A 520 1000 980 0.865 0.880 Example3 Oxygen-free copper 1500 ADC12 515 80 50 0.974 0.992 Example 4 Nickel30 ADC12 515 500 480 1.393 1.421 Example 5 Silver 20 ADC12 515 300 2901.386 1.409 Example 6 Oxygen-free copper 1500 AC4B 520 550 540 0.9270.938 Example 7 Oxygen-free copper 1500 AC9A 520 1000 985 0.850 0.860Example 8 Oxygen-free copper 1500 ADC12 515 80 65 0.957 0.975 Example 9Nickel 30 ADC12 515 500 490 1.368 1.391 Example 10 Silver 20 ADC12 515300 295 1.372 1.394 Comparative Oxygen-free copper 1500 ADC12 515 0 01.000 1.044 Example 1 Comparative Nickel 30 ADC12 515 0 0 1.453 1.498Example 2 Comparative Silver 20 ADC12 515 0 0 1.434 1.480 Example 3

In Comparative Example 1 in which the aluminum alloy plate and the metalplate (copper plate) were subjected to the solid-phase diffusion bondingwithout forming the chill layer, it was confirmed that the heatresistance further increases in comparison to the examples. In addition,when comparing Comparative Example 2 in which nickel was used as themetal plate and Examples 4 and 9, it was confirmed that the heatresistance of Comparative Example 2 further increases. Similarly, whencomparing Comparative Example 3 in which silver was used as the metalplate and Examples 5 and 10, it was confirmed that the heat resistanceof Comparative Example 3 further increases. This is assumed to bebecause a Kirkendall void was formed.

In contrast, in the examples in which the thickness of the chill layerbefore bonding and the thickness of the chill layer after bonding wereset in a range of the invention, it was confirmed that the heatresistance further decreases in comparison to the comparative examples.This is assumed to be because diffusion of a metal element thatconstitutes the metal plate is suppressed due to interposing of thechill layer having an appropriate thickness, and thus occurrence of theKirkendall void is suppressed.

In addition, in Examples 6 to 10 to which the electrical heating methodwas applied, even when the bonding was performed in the atmosphere, thealuminum alloy plate and the metal plate were bonded in a satisfactorymanner.

From the results, according to the invention, it was confirmed that thealuminum alloy member formed from an aluminum alloy having a relativelylow solidus temperature, and the metal member formed from copper,nickel, or silver are bonded in a satisfactory manner, and thus it ispossible to obtain a bonded body in which heat resistance in alaminating direction is low.

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to provide a bonded body inwhich an aluminum alloy member formed from an aluminum alloy having arelatively low solidus temperature, and a metal member formed fromcopper, nickel, or silver are bonded to each other in a satisfactorymanner, and heat resistance in a laminating direction is low, a powermodule substrate with heat sink and a heat sink which include the bondedbody, a method of manufacturing a bonded body, and a method ofmanufacturing a power module substrate with heat sink, and a method ofmanufacturing a heat sink.

REFERENCE SIGNS LIST

10, 210: Power module substrate

11: Ceramic substrate

13, 213: Metal layer

13B: Cu layer (metal member)

31: Heat sink (aluminum alloy member)

35: Chill layer

101: Heat sink

110: Heat sink main body (aluminum alloy member)

117: Metal member layer

135: Chill layer

1-3. (canceled)
 4. A method of manufacturing a bonded body that isformed by bonding a metal member formed from copper, nickel, or silver,and an aluminum alloy member formed from an aluminum alloy of which asolidus temperature is lower than a eutectic temperature of aluminum anda metal element that constitutes the metal member, wherein a chilllayer, in which a Si phase of which an aspect ratio of a crystal grainis 2.5 or less and a crystal grain diameter is 15 μm or less isdispersed, is formed on a bonding surface side with the metal member inthe aluminum alloy member before bonding, and the thickness of the chilllayer is set to 80 μm or greater, the aluminum alloy member and themetal member are subjected to solid-phase diffusion bonding.
 5. Themethod of manufacturing a bonded body according to claim 4, wherein thealuminum alloy member and the metal member are laminated, and areelectrically heated while being pressurized in a laminating direction tosubject the aluminum alloy member and the metal member to thesolid-phase diffusion bonding.
 6. A method of manufacturing a powermodule substrate with heat sink which includes an insulating layer, acircuit layer that is formed on one surface of the insulating layer, ametal layer that is formed on the other surface of the insulating layer,and a heat sink that is disposed on a surface, which is opposite to theinsulating layer, of the metal layer, wherein in the metal layer, abonding surface with the heat sink is constituted by copper, nickel, orsilver, in the heat sink, a bonding surface with the metal layer isconstituted by an aluminum alloy of which a solidus temperature is lowerthan a eutectic temperature of aluminum and a metal element thatconstitutes the bonding surface of the metal layer, a chill layer, inwhich a Si phase of which an aspect ratio of a crystal grain is 2.5 orless and a crystal grain diameter is 15 μm or less is dispersed, isformed on a bonding surface side with the metal layer in the heat sinkbefore bonding, and the thickness of the chill layer is 80 μm orgreater, the heat sink and the metal layer are subjected to solid-phasediffusion bonding.
 7. The method of manufacturing a power modulesubstrate with heat sink according to claim 6, wherein the heat sink andthe metal layer are laminated, and are electrically heated while beingpressurized in a laminating direction to subject the heat sink and themetal layer to the solid-phase diffusion bonding.
 8. A method ofmanufacturing a heat sink including a heat sink main body and a metalmember layer, wherein the metal member layer is formed from copper,nickel, or silver, the heat sink main body is constituted by an aluminumalloy of which a solidus temperature is lower than a eutectictemperature of aluminum and a metal element that constitutes the metalmember layer, a chill layer, in which a Si phase of which an aspectratio of a crystal grain is 2.5 or less and a crystal grain diameter is15 μm or less is dispersed, is formed on a bonding surface side with themetal member layer in the heat sink main body before bonding, and thethickness of the chill layer is set to 80 μm or greater, the heat sinkmain body and the metal member layer are subjected to solid-phasediffusion bonding.
 9. The method of manufacturing a heat sink accordingto claim 8, wherein the heat sink main body and the metal member layerare laminated, and are electrically heated while being pressurized in alaminating direction to subject the heat sink main body and the metalmember layer to the solid-phase diffusion bonding.